1. Field of the Invention
The present invention relates to a wavelength conversion laser device, more particularly, which achieves high wavelength conversion efficiency and increases an operating temperature range.
2. Description of the Related Art
Recently, a variety of displays and optical recording devices have seen an increasing demand for semiconductor lasers. Especially, as a semiconductor laser finds its application broadened to implement full-color in displays, there is a greater demand for a laser which exhibits low-power characteristics, and high-power capability in a visible light region.
To obtain red light, an AlGaInP or AlGaAs-based semiconductor laser can be manufactured relatively easily. On the other hand, in a process for producing green or blue light, a group III nitride semiconductor is much harder to grow than other semiconductor materials due to a unique lattice constant and thermal expansion coefficient thereof. Besides, the group III nitride semiconductor demonstrates high density of crystal defects such as dislocation, thereby undermining reliability of the laser and shortening a useful life thereof.
To solve this problem, non-linear characteristics are used to convert a wavelength. As one of methods for utilizing such non-linear characteristics, a diode-pumped solid-state laser (DPSS) has drawn attention. For example, a pump laser diode light with a wavelength of 808 nm is made incident on a crystal such as Nd:YAG to obtain a wavelength of around 1060 nm. Then the wavelength of 1060 nm is doubled in frequency using the non-linear optical crystal to produce green light with a wavelength of around 530 nm.
To date, studies on a green light source have been chiefly directed at enhancing wavelength conversion efficiency. However, to increase wavelength conversion efficiency of the non-linear optical crystal, a temperature should be regulated precisely. To assure such precise temperature control, a thermo-electric cooler (TEC) formed of a Peltier device is required, which however may significantly add to power consumption and size of the device.
Therefore, in the art, a small-sized green laser needs to achieve high wavelength conversion efficiency and a broader operating temperature range to be applicable to a portable small projector or mobile phone.